Conventionally, as a mobile communication terminal, there is known a mobile phone which executes an application program by using a direction parameter determined based on a key operation signal of a direction key. As such an application program, there is one which determines a direction parameter to be used for a process for changing a moving direction of a virtual fighter plane (virtual object) moving in a virtual game space based on a key operation signal of a direction key operated by a user. As a mobile phone which executes such an application program, there is one capable of executing an application program written in an object-oriented programming language that does not depend on a platform. For example, there is a mobile phone which is implemented with a JAVA (registered trademark, the same applies to the following description) virtal machine function and can execute an application program written in JAVA (refer to Patent Document 1). In such a mobile phone, various application programs acquired by downloading from a predetermined server can be used. The same applies to an application program which works in a BREW (registered trademark, the same applies to the following description) application execution environment.
A mobile phone which executes an application program by using a direction parameter determined based on detection data of detection means is also known. For example, in Patent Document 2, a mobile phone in which a moving direction of the mobile phone is identified by using acceleration detected by a sensor (detection means) that detects acceleration is described. In this mobile phone, based on a moving direction of the mobile phone identified from the results of detection, a moving direction (a direction parameter) of a cursor for selecting one of a plurality of input character candidates displayed on a liquid crystal display is determined and a process for moving this cursor is performed. More specifically, for example, when the mobile phone is moved to the right, according to this moving direction, a process for moving the cursor displayed on the liquid crystal display to the right is performed.
On the other hand, when a three-dimensional stereoscopic image object is displayed on a two-dimensional image screen of the display in a conventional electronic apparatus such as a mobile communication terminal or a portable game machine, it is necessary that an image of the image object viewed from a certain fixed visual point be displayed. Therefore, the control of the visual point for viewing the image object is important for displaying the three-dimensional stereoscopic image object. As a typical image display control of such a three-dimensional stereoscopic image object, there are known (1) control of display for panoramically viewing a stereoscopic image object from a visual point fixed outside the stereoscopic image object and (2) control of display for viewing a surroundings from a subjective visual point provided on a stereoscopic image object, and so on.
Describing by way of example a flight simulator on a home or business-use game machine which controls an airplane as a stereoscopic image object in a three-dimensional space by means of input from an external controller and displays the airplane on a two-dimensional screen, the image display controls of (1) and (2) are performed as follows. For example, (1) is an image display control for displaying an image panoramically capturing the airplane from a visual point fixed at the rear or side of the airplane (stereoscopic image object). The image process of (2) is an image display control in which a subjective visual point directed forward of the airplane from a virtual pilot's seat of the airplane is set, and the screen is always displayed from a visual point forward in the traveling direction even when the traveling direction of the airplane is controlled to change in response to input from an external controller.
In Patent Document 3, image display control capable of changing the visual point for viewing the stereoscopic image object is described. In this control, an image of an imitative field of view in a virtual space from a visual point set in the virtual space toward the visual line direction is displayed on display means. Then, when a user performs a predetermined touch panel operation on a touch panel, in response to the details of the operation, the visual point can be moved, the moving direction thereof can be chanced, or the visual line direction can be changed. Thereby, the position of the visual point and the visual line direction in the virtual space are changed, and the image of the imitative field of view displayed on the touch panel is changed.    Patent Document 1: Japanese Unexamined Patent Application Publication No. 2000-347867    Patent Document 2: Japanese Unexamined Patent Application Publication No. 2002-169645    Patent Document 3: Japanese Unexamined Patent Application Publication No. 2004-5272
As described above, when a process (direction changing process) for changing the moving direction of a virtual fighter plane in response to a direction parameter determined based on a key operation signal of a direction key is performed, concurrently with this process, if a process (direction changing process) for changing the visual line direction from the visual point of the game screen set in the virtual game space can be performed, a game with higher realistic sensation can be provided to the user. However, the direction parameter to be used by the conventional mobile phone for this direction changing process is determined based on only a key operation signal of a direction key, and there is no mobile phone which concurrently performs two direction changing processes different from each other according to two direction parameters. Therefore, it is not possible to provide a game with the above-described higher realistic sensation to users.
If a mobile phone which can perform the two direction changing processes concurrently with each other is realized, this is useful not only for such game application programs but also for various other application programs.
Herein, as a method for making it possible to concurrently perform the two direction changing processes, for example, it is considered that two direction keys are provided in the mobile phone to determine two direction parameters to be used in these two direction changing processes. However, in this method, it is necessary to add another direction key to the conventional mobile phone that has a direction key, and an installation space for the additional direction key must be secured on the outer surface of the mobile phone. Therefore, this results in an increase in size of the mobile phone the downsizing of which has been strongly demanded.
The description above regards a mobile phone by way of example, however, the same can be said for other mobile communication terminals the downsizing of which have been demanded.
In the conventional image display controls of (1) and (2), the operation for changing the visual point and other operations (for example, game operations) are performed by inputting by using keys and a touch panel, so that in nay cases, in terms of convenience in the user's operations, the change in visual point and real operations are alternatively selected by a user. That is, in the case of the aforementioned flight simulator, normally, the airplane is controlled by key inputs, and image display control is performed so that the visual point on the screen is changed after the key input acceptance is switched Such conflict between the operations for changing the visual point and other operations deteriorates the operability of users.
In the case of the image display control of the Patent Document 3, as described above, a user can move the visual point set in a virtual space and change the visual line direction from the visual point by performing operations on a touch panel. However, in this apparatus, operations by the user are operations on the two-dimensional plane called the touch panel, so that only by these operations, only two-dimensional directions on the plane can be determined. Therefore, by these operations, high operability involving intuitive change by a user in three-dimensional direction such as a moving direction of the visual point and the visual line direction in a virtual space cannot be realized.
Accordingly, it would be desirable to provide a mobile communication terminal and an application program which makes it possible to concurrently perform different two direction changing processes in response to an operation by a user without an increase in size of the mobile communication terminal.
It would also be desirable to provide an image display control apparatus, an electronic apparatus, and an image display control method which can realize high operability involving intuitive change by a user in three-dimensional direction such as moving direction of a visual point and visual line direction while avoiding conflict between an operation for changing the visual point in virtual space and other operations.